The aorta is the largest vessel in the body. It transports oxygenated blood from the left ventricle of the heart to every organ. The aorta extends from the heart with the aortic valve; immediately adjacent is the aortic root, followed by the ascending aorta, the aortic arch, the descending aorta, and the thoracoabdominal aorta. The abdominal section of aorta feeds the two common iliac arteries. The healthy aorta exhibits arterial compliance. That is the ability of aorta to distend and increase volume with increasing blood pressure so that the aorta yields to pressure or force without disruption. It is used as an indication of arterial stiffness.
The aortic arch is a short segment where branch vessels to the head and arms start. It has typically three branches: the brachiocephalic artery carrying the oxidized blood to the right arm, right portion of head and brain; the left carotid artery to the left head and brain; and the left subclavian artery to the left arm. There are many anomalies of the aortic arch such as the bovine arch, where there are only two branch vessels off the aortic arch. About 15% of the blood flow from the heart is supplied to the brain through these branches, and about 25% to the kidneys.
Strokes denote an abrupt impairment of brain function caused by pathologic changes occurring in blood vessels. Sudden occlusion of an artery supplying blood to the brain causes ischemic stroke. Ischemia can also occur in any organs such as the kidneys and the liver. There are two types of sources of embolic materials; the materials detached from atherosclerosis plaques of the aorta and the coagulated blood clots from the heart.
About 20% of ischemic strokes are caused by cardio-embolism. They are primarily caused by embolism of thrombotic material forming on the arterial or ventricular wall, or the left heart valves. These thrombi come away and are swept along the arterial circulation. Cardio-embolisms are generally expected when cardiac arrhythmia or structural abnormalities are present. The most common cases of cardioembolic stroke are nonrheumatic atrial fibrillation (AF), prosthetic valves, rheumatic heart disease (RHD), ischemic cardiomyopathy, congestive heart failure, myocardial infarction, post-operatory state and protruding aortic arch atheroma.
Anticoagulants are a class of drugs commonly used to prevent the blood from forming dangerous clots that could result in a stroke. Anticoagulants are frequently used in patients who are already at high-risk for stroke.
Warfarin belongs to a class of drugs called vitamin K antagonists, (VKAs) meaning that they interfere with the normal action of vitamin K, which is involved in the blood clotting process. Warfarin, the predominant anticoagulant in clinical use, reduces AF-related stroke by 64%, although this reduction is accompanied by an inherent risk of hemorrhagic complications, among which cerebral hemorrhage is especially serious. Thus up to 40% of patients with AF have the relative or absolute contraindications to anticoagulation therapy. The VKA has narrow therapeutic window and requires frequent laboratory monitoring of the international normalized ratio (INR) and subsequent dose adjustment to maintain patients within a goal INR.
The need for regular monitoring also results from the complicated pharmacokinetic profile of warfarin, the interactions with drugs, herbs, alcohol, and food, which can result in subtherapeutic (in inadequate stroke prophylaxis) or supratherapeutic (in bleeding events) drug levels. It was revealed that 44% of bleeding complications with warfarin were associated with supratherapeutic INR and that 48% of thromboembolic events occurred with subtherapeutic levels (Oake N, Fergusson D A, Forster A J, van Walraven C. Frequency of adverse events in patients with poor anticoagulation: a meta-analysis. CMAJ. 2007; 176(11):1589-94). Despite evidence-based recommendations for stroke prophylaxis with VKAs, they remain underprescribed in eligible patients with AF. Approximately 55% of patients with AF do not receive adequate stroke prophylaxis and, as result the incidence of stroke increased. Furthermore, patients who are actually treated with warfarin spend up to half of the treatment time outside the therapeutic range. This means that the full potential of warfarin to reduce stroke risk has never been fully realized nor achieved.
New oral anticoagulants (NOA) have been approved or are in development, and some are in the advanced stages of clinical research. NOAs act specifically by direct and irreversible inhibiting of the one coagulating factor. There are two classes of NOA; “direct thrombin (IIa) inhibitors” which inhibits enzyme thrombin, and “direct factor Xa inhibitors” which is central to propagation of coagulation. The NOAs have potential advantages over VKA, including a predictable anticoagulation effect that allows for fixed dosing, rapid onset and offset of action, and few drug and food interactions. In addition, they have a much wider therapeutic index compared with VKA, obviating the need for routine laboratory monitoring. However, if any bleeding occurred, the NOAs have no specific antidotes.
Prior art filter devices have not been completely successful. For example, U.S. Pat. Nos. 6,673,089 and 6,740,112 disclose a “self-expandable single-layer wire braided mesh” designed to be positioned at the bifurcation zone of the common carotid artery (CCA) to the external carotid artery (ECA). Theoretically, this braided mesh is deemed to deviate emboli to the ECA (bringing the blood in to the face) and avoid carrying it to the brain through the internal carotid artery (ICA). The rerouting efficacy of emboli into the external carotid artery (ECA) was assessed clinically by Sievert et al. in Cardiovas Intervent Radiol (2012) 35:406-412, “A novel carotid device for embolic diversion” in three patients during 6 to 14 months follow-ups and high risk of filter occlusion is observed in front of the ICA orifice.
As disclosed in U.S. Pat. No. 5,061,275, a braided self-expanding single-layer prosthesis has a limitation in the number of wires and diameter of wires in order to obtain a reasonable hoop force when it is deployed in a body lumen. The greater the diameter of prosthesis is, the more critical this limitation becomes. For example, if the diameter of prosthesis is 30 mm, the diameter of wire has to be between 220 and 300 μm and 36 to 64 wires otherwise the wall of prosthesis cannot exerts a sufficient hoop force against the wall of the vessel. Also, such device may need a large delivery system size which can compromise the femoral access.
U.S. Patent Application Publication No. 2003/0100940 discloses a stent-like protector device for filtering emboli originating from upstream sources and preventing them from entering the aortic arch's side branches that carry blood to the brain. Said filtering device consists of single-layer mesh-like tube in the form of a braided structure made of 100-160 filaments having 50-100 μm of diameter, the mesh opening width being 400-1000 μm. It has proven the difficulty to correctly position the devices at the aortic arch region because of its high rigidity and poor flexibility: it tends to remain in straight form while the aortic “arch” is obviously curved. Actually, in order to obtain fine mesh openings for a filtering device having a large device diameter designed for an aorta region, e.g. 25 to 45 mm, it should consist of either (i) a number of wires having small diameter, or (ii) long length of wires forming more than 150 degree of angle between braided wires.
Such configurations, however, may collapse when deployed in the aortic arch because it exhibits low hoop strength due to the low wire size as explain above. Also there is a technical limitation to braid such angulation between wires. High angulation leads to extensive foreshortening and misplacement of the device in the arch.
Furthermore, a single-layer braid with such window size (i.e., 400-1000 μm) may have a lack of capturing particles as reported by Order et al. in J. Endovasc. Ther. (2004) 11:211-218, particularly level of the outer side of the curve of the arch. For example, when a single-layer mesh-like tube is deployed in a curved lumen, the mesh openings at the outer side of the curve are much wider than the mesh openings in a straight configuration as shown in FIGS. 1a and 1b. 
As another problem, prior art filter devices have a lack of conformability which can lead to great risk of kinking when deformed or bent to a curve matching the curvature of the aortic arch. Such kinking further complicates the placement of the device.
Accordingly, there is a need for an implantable endoluminal prosthesis being highly compliant and exhibiting an improved emboli rerouting efficacy without complications when deployed in a curved lumen such as an in aortic arch.